A facial expression is one of the most natural communication methods transmitting a person's emotions and thoughts. A facial expression can express an emotion more quickly than when people express their feelings using words or realize their own feelings.
For example, various emotions are expressed using a change of positions of a mouth, eyes, and eyebrows.
Many studies regarding facial recognition are underway as a method for understanding a person's emotions, and recently, many studies for implementing different gestures according to each person's emotions in a personalized device such as a smart phone are underway, and studies on an interaction of a person and a robot including a service robot are actively proceeding.
Studies for allowing a robot to express various reactions according to a person's emotions are underway as part of these studies.
Accordingly, technology capable of precisely recognizing a change of an expression on a face and effectively recognizing a classification of an emotion is required.
As a conventional art regarding the technology, a method of applying an artificial neuron algorithm to a histogram-matched facial image through a normalization of lighting to recognize a facial expression is disclosed in Korea Patent No. 10-1084298.